adapted -- edited -- revised -- anecdoted -- etc. -- from
THE EVOLUTION OF USEFUL THINGS -- henry petroski -- knopf publishers -- 1992 -- chapter 11 ( pp196-201 ) -- closure before opening
(The title expresses the two problems with storing food --- sealing it -- and then getting it open again )

This book is about the "evolution" of various gagets -- and this chapter deals with the pop can. You'll remember that some of them sink and some of them float. But how are all of them made ?

How did they ever arrive at "that shape" for a pop can ?
Why is it necessary to put that "inverted dome" in the bottom of the can ?
And the most amazing question --- how do they seal the can --- and more importantly -- what strategies do we use to break the seal ?


Closure Before Opening

A good deal of our visceral sense about how physical things behave is formed in our childhood, when we have more time and fewer inhibitions about looking closely at and experimenting with the stuff that we find all about us.
My own sense of the strength of a beverage can was probably established by the time I was about seven years old. That was in the days before television occupied children's afternoons, and my friends and I looked for entertainment wherever we found it. Coming upon an empty can in the street could keep us busy till dark.

Whoever among us found the can would stomp on its side until the top and bottom curled around his shoe and locked into place like the clamps on an old roller skate. The can fit our foot like a clodhopper and, as we walked along the concrete sidewalk, made a noise heard round the block. As our group came across other empty cans, we would stomp them into more tin overshoes and have a grand time making noise and seeing who could wear the cans as shoes longest.

Getting a good fit with a tin can was no simple matter, for the cans seemed very strong to the foot of a seven-year-old, and a misdirected stomp that hit the unyielding end rather than the side of the can could be felt for days. At the same time, once the top and bottom had begun to curl around the foot, a more delicate touch was required lest the makeshift overshoe fit too tightly. Stomping cans in hard-soled shoes worked best, but we often wore canvas sneakers-high-topped Keds-and in those our feet were especially vulnerable to the revenge of the heavy tin can, if we could get the noisy toy to hold to them at all.

After such childhood experiences with it, the can as beverage container held little interest for me when I grew older. I have certainly bought my share of six-packs, but the cans themselves were not the focus of my attention . . . .


As the television commercial demonstrates, the evolution of beverage cans has outstripped previous generations' understanding of them. What had happened, while my friends and I had been growing into middle age, to turn the head-gashing instrument of the 195O's into the collapsible cream puff of the 1990's ? Like all technological change, the story of the beverage can involves considerable interplay between engineering and social factors, not the least of which are economics and the environment.

Leyden note:
Wow -- he is talking about S-T-S --- science-technology-society -- - a "theme" or "strategy" advocated for lesson planning. In this case, society has a problem -- storing food. Do we have the technology to do it ? And then there is the problem of can disposal -- littering the environment -- which gets back to science --- AND --- society --- because people don't want pollution to occur.
In the late 1950's, I was aware of few complaints about beverage cans. In fact, they were convenient but otherwise unremarkable things, although there may have been some talk about a growing litter problem. Aside from their taller shape, beer cans were not unlike the familiar tins containing food, but opened with a church key instead of a can opener. However, while consumers drank contentedly, the brewing industry was concerned about the steadily rising cost of tinplate --- the tin-coated steel out of which the cans were made. Kaiser Aluminum had initiated research-and-development efforts in the early 195O's and produced a lightweight and economical aluminum can in 1958. At the same time, the Adolph Coors Company and Beatrice Foods had joined in their own research-and-development program, and in early 1959 the first Coors beer was sold in 7 oz returnable aluminum cans the brewer made itself. ( Hamm's and Budweiser did not get their first lightweight cans ... 'til 1963, when they were able to buy them from Reynolds Metals and Alcoa, respectively. )

Leyden note:
In my lifetime i marvel at the manipulation advertisers have on us. In my "era" -- when you had a coke -- it meant a 6.5 oz bottle. Here they talk about 7 oz Coors -- but not TODAY. Everything is BIG today. Stop by for a 32 oz Coke -- super sized beer cans -- as advertisers have forced us to DRINK BIG. How come we could drink a 6.5 oz Coke and be quenched --- whereas TODAY -- it has to a Liter ?
The new cans were revolutionary not only in their raw material but also in how they were made.

Whereas the relatively heavy old tin cans comprised three pieces, an aluminum can begins with a disk of metal that is first pushed into the shape of a cup that looks not unlike a tuna can, and then it is stretched to make the taller sides of the one-piece bottom. After the can is filled, a top is crimped on. This same basic procedure is used to make today's aluminum can, though various improvements have been incorporated over the last three decades, especially in reducing the amount of metal involved. In the early years, one pound of aluminum made fewer than twenty cans; today, almost thirty cans come out of the same amount.
The thickness of the can wall is less than five-thousandths of an inch -- 0.005" about the same as a magazine cover.

The walls of the can be so thin because its contents are under Pressure.. just as a flabby balloon stiffens when it is blown up, so the carbonation in a beverage can stiffens it.

There are several steps in forming a seamless aluminum beverage can:

However, a flat can bottom would also round out like a balloon and make the can rock on the store shelf or kitchen table, and so the characteristic inward dishing of the bottom of an aluminum can is necessary.
Because a convex face is put against the pressure, the bottom acts like an arch dam in resisting the pressure of the fluid behind it, much the way the punt Joes on a champagne bottle.

Leyden note:
Think of an 'arched dam' -- like Hoover Dam. The 'curve' distributes the pressure over the arch whereas a 'straight-across-the-river-dam' is not as strong.

a PUNT mentioned above is the name of the "dent" in the bottom of a wine bottle.

The can top, on the other hand, cannot be so dished, and thus it must be thicker than the rest of the container. ( To save metal in the thicker top, aluminum cans have come to have the characteristic stepped neck, which requires a smaller diameter top: reducing the diameter of the top as little as a quarter of an inch can save 20 percent of the metal required to make it.) Although the tops on the first aluminum cans were noticeably easier to open than the steel variety, a separate opener was still required. This remained a clear disadvantage, especially when there vas plenty of beer but no church key at the family picnic. It was in such a situation that Ermal Fraze of Dayton, Ohio, found himself in 1959, when he resorted to using a car bumper to open a can. The peration evidently yielded more foam than refreshment, and 'raze is reported to have said, "There must be a better way." On subsequent night, after drinking too much coffee, he was unable

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to sleep and went to his basement workshop to tinker with the idea of attaching an opening lever to a can. He was hoping the activity would soon tire him out so that he could get to sleep, but, according to Fraze, "I was up all night and it came to me --- just like that. It was all there. I knew how to do it so it would be commercially feasible." Fraze could make such a judgment because he was the owner of the Dayton Reliable Tool and Manufacturing Company, and he had considerable experience with metal forming and scoring, the mastery of which would be essential to developing the pop-top can, for which he obtained a landmark patent in 1963. "I personally did not invent the easy-open can end," he later asserted. "People have been working on that since 1800. What I did was develop a method of attaching a tab on the can top."

Eventually a ring that functioned as a lever was riveted to a prescored tear strip . . . and a lever action enabled the ring's tab to break the can's seal. Then a pull on the ring removed the attached strip of metal from the can top in a manner not unlike the way a perforated mail --- in coupon is removed from a magazine. Because of the lever action and preferential scoring, the can opened first at the top of the hole, and a further pulling action tore the metal free of the can along the characteristic scored outline. The hole that was left extended a good distance from the edge of the can, to ( or beyond ) the center, and so, as the can was tipped for pouring or drinking, air could enter the top of the hole and allow the easy, gurgle-free exit of the contents.

The early pop-top or pop-tab can worked reasonably well, not only eliminating the need for a church key but also reducing the action of opening a can from making two separate triangular incisions on opposite sides of the top to pulling a single ring in what would ideally be one smooth motion.

Still, scoring a tear strip into a can top so that it will be easy to remove but yet strong enough to hold against the can's pressure requires some rather tricky engineering in the way the metal is formed. Some early pull tabs were being blown off prematurely by the high pressure of the carbonation rushing out of the hole made by a consumer's initial cracking of the tear strip, and so Fraze and other inventors came up with schemes to direct benignly the first whoosh of escaping gas away from the tab itself.

In the early 1960's, Ermal Fraze applied for various patents related to self-opening cans and their manufacture. There were many difficulties to overcome, for it was a touchy matter to make the can easy enough to open and yet keep the tab from pulling loose or the top from opening prematurely. He received a design patent in 1963 for this "ornamental design of a closure with a tear strip opener.

Throughout the mid-1960's, numerous patents were awarded for improvements in pull-tab devices, but then a new problem arose with environmental pollution.

By the mid-1970's, the tabs that were pulled completely off the can )p were coming under increasing attack from environmentalists, and with good reason. I recall stopping at traffic lights in those days and trying to count all the pull tabs . . . among the cigarette butts beside e road. I could never finish counting before the light changed. Camp sites and beaches were especially full of the sharp litter, hich was difficult to clean up because the small tabs passed easily rough the tines of rakes used by cleaning crews and beachcombers.

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( One young boy was reported by The New York Times as having collected 27,000 in an attempt to qualify for the Guinness Book of World Records. )

Leyden note:
a cruel hoax or LIE that was advertised in the 1970's ( 80's ? ) was that if you saved these pull tabs, they could 'purchase' minutes on a dialysis machine for some kidney patitent. So people and schools and boy scouts and girl scouts --- etc. collected them and sent them to ??????? in an effort help sick people. It was all a ruse -- a sick trick -- an urban legend.
Animals and fish, not to mention children, were swallowing the tabs, and they were cutting the feet of many a bather. Rather than discard it, some conscientious people would drop the tab in the can after opening it, but some of them required operations when they swallowed the tab with their drink. In short, there was growing concern over the failure of the pull tab to function as well as desired, and this led to another rash of patent applications for easy-open cans without removable tabs.

Leyden note:
these tabs are still used in the mideast -- jordan - golan heights - israel - palestine --- and they litter everything. When i went back the second time - xmas 1994 -- i notice the first non-pull tab openers.
There were several clever schemes to solve the loose-tab problem, and Coors was again in the forefront. It developed a two-step opening procedure, in which a protruding button of scored metal was first pressed to break the pressure seal. A second, larger button was then pressed into the can to provide a drinking hole. Restoring two-step opening procedures did not prove to be very popular, however, and their shortcomings, which included the relatively large shove required to open the can and the need to push a button through the sharp edges of a hole, were not lost on inventors. They happily included in their patent applications, as a description of the prior art, the failings of existing solutions to provide an "easy open ecology end" for the beverage can. A bewildering number of patents was being issued by the mid-1970's, but many of these were merely variations of the familiar pop tab that prevented it from being pulled all the way off.

In 1975 a patent was issued to Omar Brown of Kettering, Ohio but the rights were assigned to Ermal Fraze, the inventor whose name seems to be virtually synonymous with easy-open can patents-for a "can end with inseparable tear strip," and in a section giving some background to the invention, an especially vexing problem associated with simply folding the tear strip over the top of the can was noted:

Since most people drink the contents directly from the can, it is quite probable that the user's nose will contact a tear strip which is not fully removed from the can. If the edge of the strip is sharp, it is possible that he may cut his nose on it. On the other hand, if a sharp edge is formed around the pour spout, he may cut his lips on it. When removable pull tops came to be recognized as a significant litter problem and safety hazard, can manufacturers searched for alternatives. The Coors firm, which had pioneered the aluminum beer can came up with an "environmental package." Six cans were sold held together with drops of glue, thus eliminating the need for any other wrapping, and the cans were opened by first depressing a small button to break the pressure seal and then punching in a larger button to provide a drinking hole. This awkward design soon led to today's Familiar can top.

Leyden note:
Remember there is no such force as 'suction' -- and the small button hole mentioned above let air into the can -- so that air pressure could push the drink out the large hole.
Closure Before Opening 203

Brown's solution to the problem included recessing the pour spout, thus keeping the lips from its sharp edges, and having the opened tear strip lie flat against the can top and away from the drinker's nose. Another Ohio inventor, Francis Silver (who also assigned his patent to Ermal Fraze), protected the drinker by forming the tear strip so that it could be folded up between the can top and the pull tab. No solution proved to be wholly satisfactory, for each had its own apparent failings, not least of which was leaving too much sharp and sticky metal bunched up on top of the open can. The version of the inseparable tear strip that is on almost all bever- age cans today appeared around 1980 as a variation on the Coors push button, but operated on the lever principle through an attached tab. Since the tear-strip panel is pushed into but remains attached to the can top, both the litter problem and the danger of swallowing a tab or cutting one's nose on a sharp piece of metal are virtually eliminated.

Before environmental and worse problems with pull tabs became evident, soft-drink companies also began to package their beverages in aluminum cans. Steel cans were never totally satisfactory for soft drinks, because a church key was required to open them, and that was not in the tradition of soda drinkers. When the pull tab removed the need for an opener, the aluminum can first developed for beer was adopted for soft drinks as well. In 1965 Royal Crown ( now better known as RC ) Cola became the first to use lightweight cans; Coke and Pepsi followed in 1967. Indeed, because the absence of bottom or side seams on the new cans also made it possible to decorate them in much more elaborate ways than the old tin cans, aluminum was enthusiastically enlisted in the Cola Wars. Other advantages of the lightweight can included its lower transportation costs, its compactness, its ability to be stacked more securely, and the fact that it eliminated having to deal with empties. The one-time use of cans began to argue against them, however. By the early 19705, beer and beverage cans were being emptied at the rate of thirty billion a year in America, and ban-the-can bills were under consideration by a majority of state legislatures. Tinplated steel cans, which were still in the majority, would at least rust in landfills, but the increasingly popular easy-open aluminum cans would not. As Coors seems to have recognized from the beginning, recycling aluminum cans was not only the environmentally responsible

thing to do, it was also essential to the long-term acceptance of the new technology.

When the disposal of cans came under the growing scrutiny of environmentalists and lawmakers alike, the industry began to keep records on recycling. By 1975 about one in four aluminum cans was being recovered, and by 1990 the rate exceeded 6o percent. It is the joint goal of the Aluminum Association, the Can Manufacturers Institute, and the Institute of Scrap Recycling Industries to have a reclamation rate of 75 percent by 1995. This not only makes sense environmentally, but is also good business. Recycled cans are essential to supplement the general aluminum supply, and the collection infrastructure is now so efficient that the metal in a used can may reappear in a new one in as few as six weeks.

By 1990 aluminum accounted for about 97 percent of all beer and soda cans made in America, and about 70 percent of all U.S. beer and 50 percent of U.S. soda was packaged in them. In contrast, about 95 percent of all food cans (about thirty billion per year) remained tin-plated steel, because an economical aluminum container is not strong enough to keep its shape without the pressure of carbonation. We may begin to see more aluminum food cans in the future, however; the industry is developing strengthening techniques that include injecting liquid nitrogen into food cans to provide pressure and corrugating the can walls to provide dent resistance.

To counter its failings, the steel-can industry is engaging in research and development of its own. The economics have worked against steel beverage cans in part because they have had to be fitted with aluminum tops to be easy-opening. Even though steel has the recycling advantage of being magnetically separable, the presence of the aluminum complicates the recovery of the metals. A new ring-pull can end made of tin-plated steel may remove that objection, if it can be made as easy to open as an aluminum one and if its exposed edges can be made as smooth. The Steel Can Recycling Institute was formed in 1988 to promote the recycling of tin-plated steel cans, and it hopes that recovering food cans will protect its sponsoring industry. As an alternative strategy, steel-can manufacturers are developing plastic cans suitable for microwaves. Although perhaps a trillion aluminum cans have been produced and their contents consumed over recent decades, and even though hundreds if not thousands of patents have been issued for improvements, the form has not necessarily been perfected. The opening in (p 205) the newest pop tops is generally oval-shaped and does not extend completely to the edge of the can or toward the middle, where the ring is attached. Hence, pouring and drinking are a bit tricky: tipping a full can too severely does not allow air to enter so readily, and a nearly empty can must be tipped almost upside down to get at the last of the beverage, so it is nearly impossible to empty the can completely. We tend to adapt to available technology, however, and we seem to have come to tip our cans in the same way we came to tip our bottles, at just the right angle for the level of the contents. However, unlike bottles, whose narrow necks gave us plenty of room to maneuver, the tabs attached to pop-top cans do come up to meet our noses if we are not careful. They no longer pose a threat of cutting us, but they do restrict how far the container can be tilted, and so we must compensate with a greater angle in our necks.

But the interest of inventors is not limited to anatomical inconve- niences. Among the functional imperfections of the familiar beverage can are its inability to be reclosed if its contents are not all drunk at once. Cans of coffee, nuts, and even tennis balls typically come with plastic lids that can be used to reseal the opened container, but beverage cans generally do not.

Leyden note: you are invited to invent a re-sealable metal container.